Support member for use with semipermeable membrane

ABSTRACT

A support member for use in a coil dialyzer to support an elongated, tubularly-shaped, semipermeable membrane is disclosed herein. The member is embossed and has generally angularly-extending parallel ribs on both sides of the web. The ribs are arranged so that on each side there are high ribs and low ribs positioned between said high ribs.

This is a continuation, of application Ser. No. 620,543, filed Oct. 8,1975, now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to mass transfer devices of the type whichinclude a semipermeable membrane; and more particularly, to dialyzers ofthe type used in artificial kidney systems.

Artificial kidney systems are used to treat a patient's blood so as toremove waste products therefrom. One type of dialyzer used in suchsystems is commonly referred to as a coil dialyzer. It includes aflattened, tubularly-shaped, semipermeable membrane of a material, suchas cellophane or polycarbonate, which along with an appropriate supportmember, is wound or coiled about a center core and enclosed in acylindrical housing. Blood from a patient enters the dialyzer through aninlet in the core, flows through the dialyzer inside the membrane andexits the dialyzer through an outlet. Dialysis solution flows in acrosswise direction through the housing and between the wound supportand membrane.

The dialysis solution contacts the membrane, and due to the differencein waste product concentration between the blood and the dialysissolution, the waste products, such as urea and creatinine, diffuse fromthe blood through the membrane and into the dialysis solution.

During treatment of blood in a dialyzer, water is removed from the bloodby virtue of a process known as ultrafiltration. The amount of waterwhich is removed is related to the difference in blood pressure anddialysis solution pressure on opposite sides of the membrane. Existingdialyzers operate at relatively high blood pressure levels which isrelated to the size and shape of the membrane and the membrane support.This high pressure may result in undesirably high and/or variable levelsof water removal.

It is an object of this invention to provide a dialyzer wherein waterremoval is controllably maintained at a low level.

In existing dialyzers the conduits which carry blood to and from thedialyzer may become kinked where they enter and exit the dialyzer.Further, in existing constructions dialysis solution exits from the topof the dialyzer. This results in an esthetically displeasing "sloshing"sound.

It is another object of this invention to provide a dialyzer structurewherein kinking of the blood conduits is minimized and "sloshing"eliminated.

The cellophane membrane is relatively fragile and may rupture or tearduring assembly of the dialyzer when the membrane is sealed and isconnected to the blood conduits. It is yet another object of thisinvention to provide an improved end seal and connector which minimizesmembrane damage.

Furthermore, existing dialyzers are relatively expensive to manufacture,and it is therefore another object of this invention to provide adialyzer which is less expensive to manufacture.

These and other objects of this invention will become apparent from thefollowing description and appended claims.

SUMMARY OF THE INVENTION

There is provided by this invention a dialyzer for use in an artificialkidney system, which operates at low controllable ultrafiltrationlevels, reduces conduit kinking at the dialyzer inlets and outlets,eliminates "sloshing", and includes an improved end seal and connectorconstruction.

The dialyzer includes a membrane and a membrane support member, whichare constructed to provide a low blood pressure level and therebyassures low controllable levels of ultrafiltration. The dialyzer bloodinlet and outlet conduits are generally axially aligned with respect tothe housing so as to minimize kinking and the dialysis solution outletis positioned so as to eliminate "sloshing".

The dialyzer includes a folded end seal for closing the ends of themembrane and a blood button arrangement for connecting the membrane tothe blood inlet and outlet. These features contribute to minimizingmembrane damage.

Furthermore, many of the dialyzer components can be fabricated by fastand economical mass production techniques, such as extruding, embossingor injection molding, which reduce the cost of the dialyzer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a dialyzer made in accordance with theinvention;

FIG. 2 is a fragmentary longitudinal cross-sectional view takensubstantially along line 2--2 of FIG. 1;

FIG. 3 is a transverse cross-sectional view taken substantially alongline 3--3 of FIG. 1;

FIG. 4 is an exploded perspective view of an inlet jack assembly for usein the dialyzer;

FIG. 5 is a top plan view of a blood button connector for use with theinlet jack assembly;

FIG. 6 is a longitudinal cross-sectional view taken substantially alongline 6--6 of FIG. 5;

FIG. 7 is an exploded, fragmentary sectional view showing the connectionbetween the inlet jack assembly and semipermeable membrane;

FIG. 8 is a fragmentary perspective view of a support member and amembrane for use in the dialyzer;

FIG. 9 is a sectional view of the support member taken substantiallyalong line 9--9 of FIG. 8;

FIG. 10 is a sectional view similar to FIG. 8 but showing an alternativesupport member configuration;

FIG. 11 is a plan view of a support member of the type shown in FIGS. 9and 10;

FIG. 12 is a sectional view taken substantially along line 12--12 ofFIG. 8;

FIG. 13 is an exploded perspective view of an outlet jack assembly foruse in the dialyzer showing the inner side of the outlet jack;

FIG. 14 is a perspective view of the outer side of the outlet jack;

FIG. 15 is a transverse cross-sectional view taken substantially alongline 15--15 of FIG. 13;

FIG. 16 is a perspective view of a top cap for use in the dialyzer;

FIG. 17 is a fragmentary and exploded perspective view showing a portionof the dialyzer housing and core assembly; and

FIG. 18 is a perspective view of a bottom cap for use in the dialyzer.

DESCRIPTION OF THE PREFERRED EMBODIMENT General

Referring now to the drawings, and more particularly FIGS. 1-3, there isshown a dialyzer 10 having an outer casing which includes a hollow,elongated, pear-shaped, transparent, plastic housing 12, an upper or topend cap 14 and a lower or bottom end cap 16. The dialyzer also includes:a centrally-positioned, cylindrical, core assembly 18; an elongatedplastic support member 20 and an elongated membrane 22, which are woundabout the core assembly; and an outlet jack assembly 24. An innercentrally-positioned, flexible, plastic blood inlet tube 26 extendsthrough the upper cap 14 and cooperates in directing blood entering thedialyzer into the membrane 22. An outer blood outlet tube 28 extendsthrough the upper cap and directs blood exiting the membrane to a pointoutside the dialyzer. The lower end cap 16 also includes a dialysissolution inlet 30 and a dialysis solution outlet 32.

Generally speaking, blood from a patient who is being treated enters thedialyzer through the blood inlet tube 26, flows through the coiledtubular membrane 22, and exits the dialyzer through blood outlet tube28. The dialysis solution enters the dialyzer through the inlet port 30,flows upwardly between the windings of the membrane and the membranesupport, contacts the membrane so as to receive metabolic waste productsand water from the blood, and exits the dialyzer through the outlet 32.

The Core Assembly

The inner core assembly 18, as shown in FIGS. 2, 3 and 17, includes anelongated, C-shaped core 34, which is extruded from a plastic, such asstyrene, and a separate inlet jack assembly 35. The core 34 is shaped toprovide an offset somewhat U-shaped membrane retaining slot 36 and asmaller offset support member retaining slot 38. Both of these slotsextend inwardly toward the center of the core and open outwardly towardthe outside of the core. The facing edges 40 and 42 of the core eachincludes a semicircular jack-receiving slot 44 or 46 and define anelongated inlet-jack-receiving gap.

The inlet jack assembly 35, as shown in FIGS. 3, 4 and 7, includes theblood inlet tube 26, an inlet elbow 48, and an elongated molded inletjack member 50. The jack member is constructed to fit within the gapdefined by the core edges 40 and 42 and be bonded to the core 34. Thejack member has a curved central body portion 52 and a pair of sideflanges 54 and 56, which slidably and sealingly engage thejack-receiving slots 44 and 46. The outer surface of the central bodyportion of the jack is curved in a manner complementary to the curvatureof the core so as to form a generally cylindrical core assembly.

A short, integral, boss-like structure 58 is centrally positionedbetween the ends of the jack member on the back side thereof and extendstoward the center of the core assembly. A tapered passageway 60 extendstransversely through the body portion 56 and through the boss 58. Anintegrally-molded, countersunk, O-ring-receiving, recess 62 is formed inthe body portion 56 and surrounds the outer terminal end of thepassageway 60 and a plurality of molded blood distribution grooves, suchas 63 and 64, extend radially from the O-ring recess. A taperedinternal, annular snaplock shoulder 65 extends inwardly into thepassageway adjacent the other end of the passageway.

The elbow 48 is bonded to outlet end of the blood inlet tube 26 and alsotelescopically engages and is bonded to the boss 58 so as to directincoming blood flow from the tube 26 into the passageway 60.

The Membrane and The Support Member

Referring now to FIGS. 3, 8-12 and 17, the membrane 22 is an elongated,flattened tube of a semipermeable material, such as cellophane or acellulose derivative sold under the trade name Cuprophan. The membraneis coiled or wound about the core assembly and serves as a conduit forthe passage of blood through the dialyzer from the core assembly 18 tothe outlet jack assembly 24. This membrane separates the blood anddialysis solution but permits blood waste products and water to passfrom the blood into the dialysis solution contacting the membrane. Italso permits preselected substances placed in the dialysis solution topass through it and into the blood.

The support member is longer and wider than the membrane and may be ofthe conventional open mesh screen type as disclosed in U.S. Pat. No. Re.27,510 or of an embossed type, such as is disclosed in U.S. Pat. No.3,687,293. Such an embossed support includes an imperforate center webhaving equal-height, membrane-engaging ribs on each side of the web.

The member 20 shown in FIGS. 9 and 10 is embossed and is wound about thecore along with the membrane 22 so as to space the convolutions orwindings of the membrane from each other to assure that dialysissolution flows between the convolutions, and that the solution contactsthe membrane walls or surfaces. The support member 20 as shown herein isa fluid impermeable sheet of an appropriate material which has beenembossed, on both sides, with an appropriate pattern of supporting andchannel forming ribs. The support member 20 includes a central web 66having, on each side, a plurality of elongated ribs, such as 68, 70, 72,74, 76 and 78, that extend angularly across the web from onelongitudinal edge to the other.

The ribs on each side form an acute angle of about 60 degrees to thelongitudinal edge of the web. However, the ribs on opposite sides extendin opposite directions. This causes the ribs to overlap in adiamond-like pattern, where the obtuse or included angle formed ispreferably about 120 degrees. However, that angle may be between about60 degrees and 140 degrees. The rib patterns on each side of the memberare identical, except for direction, and repeat in a pattern of onelarge rib and four smaller rounded-tip ribs.

The preferred support member 20, as shown in FIG. 8, is fabricated of asoft, low-modulus-of-elasticy material, such as medium densitypolyethylene. In the preferred rib pattern, the larger or high ribs 68and 78 are flat-topped, have a trapezoidal cross-section, are spacedabout 0.323 inches apart and are about 0.021 inches tall. The smaller orlow ribs 70, 72, 74 and 76 are triangularly-shaped, having roundedmembrane-engaging tips, are each about 0.012 inches tall, and aresubstantially equally spaced between the high ribs. The total thicknessof the support member is about 0.047 inches. The rib height and spacinghave been selected to form an appropriate blood path in the membranewhich assures a low blood pressure and substantially equal dialysissolution flow rates in the channels defined by the ribs and membrane.

Referring now to FIG. 10, there is shown an alternate support member 80,which has a different rib pattern or configuration. In this support allof the ribs 82, 84, 86, 88, 90 and 92 are triangularly shaped and haveslightly rounded membrane-engaging tips. The two large or high ribs 82and 92 are each about 0.023 inches tall and are spaced apart, oncenters, about 0.323 inches. The ribs 84 and 90 which are adjacent thehigh ribs are each about 0.012 inches high and the innermost ribs 86 and88 are about 0.016 inches tall. The lower ribs are substantially equallyspaced between the high ribs 82 and 92. The total thickness of themember 80 is about 0.050 inches. This particular member is fabricatedfrom a stiffer, higher modulus material, such as high densitypolyethylene.

As can be seen, the rib configuration can be varied so as to providemulti-rib levels which permit a wide range of control over blood pathgeometry.

From FIG. 12 it will be seen that when wound, the support member engagesthe membrane on opposite sides and due to the angular attitude of thesupporting ribs, the large ribs, such as 68 and 78, overlap so as toform essentially a plurality of point contacts which grasp and hold themembrane therebetween. Since the ribs are angularly disposed, theoverlapping ribs cannot interfit between one another (otherwise known asinterdigitation) which could prevent or inhibit flow of blood and/ordialysis solution.

The angle ribs in either of the support members provide a clear flowchannel for the dialysis solution to flow angularly from onelongitudinal edge of the support member to the other. The shortersupporting ribs engage the membrane in a manner so as to definesubstantially equal flow channels and to prevent the membrane fromcontacting the web.

The inner end of the support member 20 is secured to the core assemblyby fitting its inner transverse edge into the support member receivingslot 38.

Membrane End Seal

The membrane 22 is a flattened tubular member which must be sealed ateach end in order to provide a leak-free conduit between the blood inlettube 26 and blood outlet tube 28. Referring to FIGS. 3, 8 and 17, aparticularly effective end seal is achieved by forming end flaps, suchas 22a, and folding the flaps against the body of the membrane. Such afold forms a transverse fold line 22b which extends from onelongitudinal edge of the membrane to the other longitudinal edgethereof. Preferably the fold line is substantially perpendicular to thelongitudinal edges of the membrane.

At the core assembly end, the membrane 22 is folded so as to form theflap 22a which is folded outwardly onto the membrane body so as to formthe inner fold line 22b. The fold is then positioned in thewedge-receiving groove 36 for maintaining the fold line. An elongatedwedge 94 is pressed into the groove 36 so as to securely retain the foldand to secure the membrane end in position on the core as it is wound.The wedge 94 matingly fits within the groove and includes a shaped outersurface 94a, which conforms to the outer configuration of the core.

Blood Button Connector

A molded plastic inlet blood button connector 100 (as shown in FIGS.4-7), connects the inlet jack passageway 60 with the membrane interiorfor directing blood entering the dialyzer into the membrane. The inletblood button connector 100 is a hollow, rivet-shaped member having aconvex crown or cap portion 102 and a tapered body or barrel portion 104having a bore or passage 105 which extends through the barrel and cap.The barrel includes a reduced diameter section or recess 106 and atapered retaining lip 108 adjacent the end of the barrel opposite thecap. The lip and reduced diameter section define a snap-lock groovewhich cooperates with the inlet jack aperture shoulder 65 for snappinglyengaging and securing the blood button connector to the inlet jack.

Six radial blood distributing grooves, such as 110 and 112, are providedin the cap for cooperation with the membrane in distributing bloodradially outwardly from the passageway 105.

An O-ring seal 114 is seated in the recess or groove 62 surrounding thepassageway 60. The O-ring 114 is an elastomeric sealing member whichcooperates in providing a leak-free connection between the passagewayand membrane and which is compressed when assembled so as to resilientlyengage: the membrane adjacent the underside of the blood button cap 102and hold it against the cap; the jack; and the blood button barrel 104.The O-ring 114 is of a non-aging, resilient, creep-resistant,elastomeric material, such as silicone, which minimizes seal leakage.

In order to install the inlet blood button connector 100, a small, roundaperture 116, is cut into a side wall of the membrane 22 adjacent theinner end thereof and approximately centered between the membrane edges.The blood button is then slipped into the membrane from an open end,before the end is sealed, and the barrel 104 is inserted through theaperture 116 so that the cap 102 is positioned against the inside wallof the membrane 22 and the barrel extends outwardly therefrom. The bloodbutton is then urged inwardly and snap-locks with the shoulder 65 in thejack bore. The blood button cap firmly holds the portion of the membranecontacting the underside of the cap against the inlet jack and againstthe O-ring so as to minimize seal leakage.

With the end seal secured by the inlet jack wedge 94, a substantiallyleak-free seal and conduit system is provided for blood flowing throughthe inlet tube 26, the inlet elbow 48, the inlet jack passageway 60 andthe blood button connector 100.

An advantage to the connector 100 is that the membrane 22 is heldagainst the core assembly 18 and any force applied to the inlet tube istransmitted to the core assembly 18 rather than directly to the membrane22.

With the membrane end sealed, the blood button 100 secured to the inletjack 50, and the support member 20 positioned in the support memberrecess 38, the member 20 and membrane 22 are wound together about thecore until the predetermined length of the support member and membraneare exhausted. Normally, the support member 20 is both longer and widerthan membrane 22. The support member 20 and membrane 22 are then securedto the outlet jack assembly 24. Furthermore with both the membrane andsupport secured to the core assembly, relative movement between themembrane and member is reduced which further minimizes possible damageto the membrane.

Outlet Jack Assembly

The outlet jack assembly 24, as shown in FIGS. 2 and 3, includes anelongated molded outlet jack member 120, as shown in FIGS. 13-15. Thejack has a concave inner face 122, which is constructed to fit againstthe outermost winding of the membrane 22. The inner face includesseveral longitudinally extending sections for cooperation with themembrane which it contacts. The first section 124 is a blood inlet pathdefining section which includes a plurality of spaced parallel ribs,such as 126 and 128, which extend inwardly from the leading edge of thejack. These ribs 126 and 128 serve to direct blood flow in the membranefurther along the inner face of the outlet jack.

A recessed blood flow collection path or channel 130 is positionedadjacent the blood path section 124 and extends for the full length ofthe jack. A blood button receiving bore and blood flow passageway 132 iscentrally positioned in the blood flow channel. A countersunk O-ringreceiving recess 136 surrounds the bore and faces toward the inside ofthe dialyzer. The bore 132 extends through an outwardly extending boss134 on the back side of the outlet jack. An elbow 138, which is bondedto the inlet end of the outlet tube 28, telescopically engages and isbonded to the boss 134, and directs blood flowing from the passageway132 to the blood outlet tube 28.

An inwardly facing fold-retaining and wedge-receiving groove 140 ispositioned on the side of the blood flow channel 130 opposite the blooddirecting ribs 126 and 128.

The bottom end of the jack is defined by a bottom fin or plate 142,which extends rearwardly or outwardly from the inner face 122. A topplate or fin 144 extends across the top of the jack, but it will benoted that the top plate is recessed at a position above the boss 134for cooperation in positioning the blood outlet tube 28. A pair ofelongated rigidifying ribs 146 and 148 on the outer side of the jackconnect the top and bottom fins. Top and bottom locating pins 150 and152 project from the fins 144 and 142, respectively.

The membrane 22 is connected to the outlet jack 24 with an outlet bloodbutton connector 154, which is substantially identical with thepreviously described inner blood button connector 100.

An O-ring 156, similar to the O-ring used with the inlet jack assembly,is positioned in the O-ring groove 136 and the outlet blood buttonconnector is snap-locked to the outlet jack to hold the membrane to theoutlet jack in the same manner as the inlet jack. The membrane isend-sealed by a fold seal of the type described in connection with theinlet jack with the main difference being that the outer flap ispositioned on the inner side of the membrane. The outlet jack wedge 157retains and holds the end seal in position. In the assembly, the outerend of the support member thereof is positioned back behind the innerface of the outlet jack.

Housing and Assembly

As seen in FIGS. 2-3 and 16-18, once the core assembly 18, supportmember 20 and membrane 22 and outlet jack 24 are assembled, the housing12 is slipped over the assembly so as to retain it in position with theoutlet jack positioned within the protruding portion 12a which extendsalong the side of the housing 12. The top and bottom caps 14 and 16 aremounted to and sealingly engage the ends of the housing.

The top cap 14 is molded so as to provide a centrally positioned bloodinlet tube aperture 170 and an offset blood outlet tube aperture 172.The blood inlet tube 26 extends through and sealingly engages the inletaperture 170, and the blood outlet tube 28 passes through and sealinglyengages the outlet aperture 172. The cap 14 also includes the spacedparallel outer and inner walls 174 and 176, which define a groove 178therebetween for sealingly engaging the top edge of the housing 12.

Three cap ribs 180, 182 and 184 extend inwardly from the cylindricalportion of inner wall 176 toward the blood inlet tube aperture 170. Eachof the ribs includes a tapered and notched inner edge or shoulder 186,which is adapted to engage the top edge of the core assembly forcentrally positioning the core assembly in the housing. The lowersurface, such as 181, of each rib engages the top edge of the woundmembrane and support so as to prevent telescoping or upward movement ofthe membrane and support.

A small curved, outlet-jack engaging wall 188 is molded across theprotruding portion of the cap for general alignment with the inner face122 of the outlet jack. A pin-receiving socket 190 is also moldedadjacent the wall and is for receiving the top pin 150 on the top end ofthe outlet jack.

The bottom cap 16 includes parallel outer and inner peripheral walls 192and 194, which together define a peripheral groove 196 for cooperativesealing engagement with the bottom edge of the housing 12. A small,curved outlet jack engaging wall 198 is molded across the protrudingportion of the cap and is generally shaped to conform to the inner faceof the outlet jack. An outlet jack pin-receiving socket 200 is moldedalong the wall for receiving the outlet jack bottom pin 152.

A tubular inlet 202 is molded to the outer and underside of the bottomcap and includes a bore 204 which communicates with the inlet 30. Theoutlet 32 is formed by a large aperture in the cap. The aperture issurrounded by a core assembly locating and receiving shoulder 206 andcollar 208. It should be noted that the inlet bore 204 is positionedbetween the collar 208 and wall 198.

With the housing 12 in place, the inlet tube 26 and outlet tube 28 arethen passed through the upper cap and the upper cap is fitted downwardlyagainst the top edge of the housing, the top of the core assembly andthe top of the outlet jack. In a similar manner, the bottom cap isfitted against the bottom edge of the housing and against the coreassembly and the outlet jack. It will be noted that with such anassembly both the blood inlet tube 26 and blood outlet tube 28 extend ina generally parallel and axial arrangement whereby kinking and bendingof the tubes are minimized.

Once the core assembly 18 and outlet jack assembly 24 are fixed inposition in the housing by the top cap 14 and bottom cap 16, any forcesapplied to the tubes 26 or 28 are transmitted through the core or jackassemblies to the caps and housing. Thus, those forces are not applieddirectly to the membrane and membrane rupture is reduced.

Operation

As seen in FIG. 2, incoming dialysis solution flows, as indicated byarrow 210, upwardly through the inlet 30. The dialysis solution thenflows around the core assembly locating collar and upwardly through thewound membrane and support member into the center of the core assembly18 as indicated by arrows 216 and 218. From there the dialysis solutionflows downwardly and exits the dialyzer through the outlet 32. Thus thedialysis solution flow path forms a generally inverted U-shape.

Blood entering the dialyzer through the tube 26 flows downwardly throughtube 26, as indicated by arrow 220, through the elbow into the inletjack and through the blood button bore into the membrane 22. Blood thenflows inside the membrane in a spiral path around the core until itreaches the outlet jack assembly 24. At the outlet jack assembly, theblood is directed by the blood directing ribs, such as 126 and 128, intothe blood flow channel 130 and hence to the blood button connector 154.Blood entering the blood button connector 154 flows through the outletjack passageway 132 into the outlet elbow 138 and from there through thetube 28.

The blood is prevented from flowing out of the end seals by virtue ofthe folded-and-locked end seal arrangements, both at the inlet jack andoutlet jack. The possibilities of blood leak have been minimized by theselection of the support materials and rib structure. Dialysis solutionflow into the outlet jack area is minimized by the engagement of thearcuate walls 188 and 198 with the outlet jack. However, some dialysissolution flow into the outlet jack area can be tolerated.

It will be appreciated that numerous changes and modifications can bemade to the embodiment disclosed herein without departing from thespirit and scope of this invention.

What is claimed is:
 1. A flexible support member for use in a coildialyzer to support a tubularly shaped, semipermeable membrane, saidsupport member comprising: an imperforate fluid impermeable web; meanson both sides of said web defining a plurality of generally parallel,membrane engaging ribs for supporting said membrane and for maintainingsaid membrane in spaced relation to said web, said ribs on at least oneside of said web including a plurality of first ribs spaced from eachother and a plurality of second lower ribs, with at least one lower ribbeing positioned between each pair of adjacent first ribs, said firstribs and said lower ribs being arranged on at least one side of said webwith at least said first ribs being configured to prevent ribs on theother side of said web from extending into spaces defined between saidfirst ribs when said one side is positioned opposite the other side insupporting said membrane.
 2. A support member as in claim 1, whereinsaid first and said second lower ribs are arranged in generally angularrelation to the length of said member and extend from one longitudinaledge of said member to the other longitudinal edge.
 3. A support memberas in claim 2, wherein said member includes first ribs and second lowerribs on the other side of said web in generally overlapping relationwith said ribs on said one side so as to form a diamond-shaped pattern.4. The support member according to claim 1, wherein at least said firstribs on said one side are elongated and arranged at an angle to ribs onthe other side of said web.
 5. A coil dialyzer having an elongatedflexible support member to support an elongated tubularly shaped,semipermeable membrane, said support member comprising, an imperforatefluid impermeable web; said web defining on both sides thereof aplurality of generally parallel membrane engaging ribs for supportingsaid membrane and for maintaining said membrane in spaced relation tosaid web; said ribs including first ribs and second lower ribs on bothsides of said web with at least one second lower rib positioned betweeneach pair of adjacent first ribs, said ribs being arranged in agenerally angular relation to the length of said member and extendsubstantially from one longitudinal edge of said member to the otherlongitudinal edge; and said ribs on opposite sides being in generallyoverlapping relation so as to form a diamond-shaped pattern.
 6. Anelongated flexible support member for use in a coil dialyzer to supportan elongated, tubularly-shaped, semipermeable membrane, said supportmember comprising: an elongated imperforate fluid impermeable web; meanson at least one side of said web defining a plurality of elongated,generally parallel, membrane engaging ribs for supporting said membraneand for maintaining said membrane in spaced relation to said web, saidribs extending substantially across the width of said member andincluding a plurality of first high ribs spaced from each other and aplurality of second lower ribs, with at least one lower rib beingpositioned between each pair of adjacent high ribs.
 7. A support memberas in claim 6, wherein said ribs are arranged in generally angularrelation to the length of said member and extend from one longitudinaledge of said member to the other longitudinal edge.
 8. A support memberas in claim 6, wherein said member includes membrane engaging ribs onboth sides of said web, with the ribs on opposite sides being ingenerally overlapping relation so as to form a diamond-shaped pattern.9. A support member as in claim 6, wherein: each high rib has agenerally trapezoidal cross-sectional shape; and each lower rib has agenerally triangular cross-sectional shape and a rounded membraneengaging tip.
 10. A support member as in claim 6, wherein each of saidlower ribs is substantially the same height.
 11. A support member as inclaim 6, wherein said ribs are substantially equally spaced from eachother.